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Mixture control during aerobatics

Posted By:
Sam Shifrin
IAC Member
9
Posts
5
#1 Posted: 3/10/2010 14:59:00

What are you "guys and girls" doing with the mixture control settings during aerobatics?  Constant speed prop and fixed pitch?



Craig Christopher
IAC Member
5
Posts
1
#2 Posted: 3/11/2010 18:40:47

Full rich, full time,  till shut down.



Richard Rihn
IAC MemberNAFI Member
1
Post
1
#3 Posted: 3/11/2010 18:46:22

I do aerobatics full rich.  However I rarely ever fly above 5000 feet.  I feel that excess fuel helps keep cylinder head temperatures down while the aircraft is developing full power at low airspeeds.  Idle mixture is critical to prevent engine  "richening out" during spins or tail slides.



Ray Ordorica
Homebuilder or Craftsman
36
Posts
1
#4 Posted: 3/11/2010 23:36:39

What about at higher altitudes? I fly in the Idaho mountains, and ground level is 4000 feet. I plan to take aerob. lessons soon and will be doing my flying at about 6000-7000 feet MSL, and I fly a Citabria 115-hp. Thoughts, please.

........Ray



RayO
Carl Alburn
8
Posts
4
#5 Posted: 3/12/2010 13:35:05

Most of my 38 years of flying has been at higher elevations, presently out of the Fort Collins/Greeley area, formerly out of Laramie.  At higher elevations, you should not be using full rich for aerobatics, any more than you should use full rich for normal flight.  You should be leaning on the ground for take off, and if you will be remaining within 2-3000' AGL for your aerobatics, I would recommend that you leave the mixture at your take-off setting.  If you decide for safety reasons to be significantly higher, then I would recommend leaning for the lowest altitude you will be flying.  For instance, if your "window" is from 8-10,000' MSL, lean for full power at 8,000 and then leave the mixture alone.

Caveat: I haven't instructed in more than 25 years, and I never instructed aerobatics. However, I learned aerobatics out of Boulder, and one of the airplanes I flew was a 150 hp fixed pitch Decathlon--the other was a 180 hp CS Super Decathlon. You will spend a lot of time at full power in a 115 hp Citabria, so your mixture needs to be rich enough to prevent engine damage but lean enough to give you full power.  That will likely take a bit of experimenting to get exactly right, and without an engine analyzer, you probably can't.  You might come close with an EGT.  My method above will probably preserve your engine better than trying to adjust it "on the fly" for each maneuver.

Cary



Ray Ordorica
Homebuilder or Craftsman
36
Posts
1
#6 Posted: 3/12/2010 23:52:51 Modified: 3/12/2010 23:57:08

Cary,

Thanks for the note. I learned to fly in Hamilton, MT (K6S5) and we always leaned on the ground and left it lean until landing. The altitude of that airport was 3600 or so. Flying now out of Salmon (KSMN) I also lean the Citabria on the ground and keep it there until I land, never enrichening it for landings. When I go X-country I use the onboard EGT to get a better lean, and it saves gas.

Around here the airports are in valleys surrounded by severe mountains, so everything is generally higher than the home base. Clever pilots get pretty well up in the air before attempting to cross said mountains. Mountain turbulence is quite unbelieveable, and also very unpredictable. I expect I'll have a base of at least 7000 for my "window." I agree, the 115-hp engine will be working pretty hard all the time, and your suggestions about leaning for the lower altitude make perfect sense.

Thank you very kindly for your suggestions.

......Ray

PS: Here's a photo of the Salmon valley looking south.
 

 



Files Attachment(s):
SALMON VALLEY.JPG (112458 bytes)
RayO
Mark Rogge
IAC Member
2
Posts
1
#7 Posted: 3/15/2010 19:11:07

Ray,

I used to fly my first Super Decathlon over Payette Lake in McCall Idaho.  Field elevation is 5000'.  So, I was generally between 7000' and 10,000' msl.  I would lean for best power at field elevation during run-up and not touch the mixture until after landing.  I had an engine monitor and gami injectors so it was possible to do it accurately.

Mark



Mark N28EJ
Ray Ordorica
Homebuilder or Craftsman
36
Posts
1
#8 Posted: 3/16/2010 00:43:22

Hey, Mark,

That sounds like a better idea than trying to do so at altitude. Per one of the earlier posts here your ground-settiing procedure would make the mixture a bit on the rich side at altitude, which ought to help keep the engine on the cool side during hard work. With minimal engine-monitoring instruments that might be a better method than trying to do it all in the air. Thanks for the tip.

.......Ray



RayO
#9 Posted: 4/15/2010 13:58:13

Full rich is usually the norm. To busy to be monitoring gauges during abrupt manuevers or altitude changes. By having full rich, I can concentrate just on flying!  My field is 640 ft. msl



N202MK Giles 202 S/N 11 Owner
Sam Shifrin
IAC Member
9
Posts
5
#10 Posted: 4/15/2010 20:03:41

Thanks all, full rich it is. 

Sam



Dale Sorensen
Homebuilder or Craftsman
1
Post
0
#11 Posted: 4/17/2010 08:52:38

I fly a Steen Skybolt, 540 with a pressure carburetor,  I fly in Utah and I lean on the ground and don't usually lean when doing aerobatics.  My airport elevation is 4,229.